(1) Field of the Invention
The present invention relates to a method and apparatus for recording the respiratory sounds of a horse during exercise of the horse to determine whether the horse suffers from an upper airway obstruction condition. In particular, the present invention relates to a method and apparatus for recording the respiratory sounds of a horse during exercising by positioning a portable microphone adjacent the horse's nostrils which is connected to a recorder.
(2) Description of the Related Art
Horses commonly suffer from several different upper airway obstructive diseases, including left laryngeal hemiplegia (LLH), dorsal displacement of the soft palate (DDSP), pharyngeal collapse and entrapment of the epiglottis. Left laryngeal hemiplegia and DDSP are by far the most common causes of upper airway obstructions in horses and these conditions have an estimated prevalence of approximately 10% of horses. Left laryngeal hemiplegia is caused by a neuropathy of the left recurrent laryngeal nerve. This condition results in the paresis of the associated arytenoid cartilage. During exercise, this cartilage cause airway obstruction, respiratory noise production and exercise intolerance (Seeherman, H. J., Left Recurrent Laryngeal Neuropathy, In: "Current Therapy in Equine Medicine 4" N. E. Robinson (ed) W. B. Saunders, Philadelphia, pages 404-407 (1997)). The cause of dorsal displacement of the soft palate is presently unknown. Experimentally, the disease is reproduced by blockade of the pharyngeal branch of the vagus nerve. Because this nerve branch runs in close proximity to the retropharyngeal lymph nodes, it is thought that in naturally occurring cases, DDSP is caused by infection of these lymph nodes and consequent damage to the nerve branch. Like in cases with LLH, DDSP causes airway obstruction, respiratory noise production and exercise intolerance in affected horses (Ducharme, N. G. et al, Intermittent Dorsal Displacement of the Soft Palate, In: "Current Therapy in Equine Medicine 4", N. E. Robinson (ed) W. B. Saunders, Philadelphia, pages 415-418 (1997)). In many cases, upper airway conditions can not be diagnosed in the resting horse as the conditions only occur during exercise. Upper airway obstructions are often associated with abnormal respiratory noise. Respiratory sounds in exercising horses are difficult to evaluate because the trained observer is not always in an optimal location. Furthermore, the respiratory sounds are obscured by extraneous noises such as hoof beats, wind noise, or sounds associated with treadmill operation. Presently, diagnostic methods are time consuming, highly technical, and expensive. The old method of diagnosing upper airway conditions in horses involves fiber optic endoscopy. In this technique, a fiber optic endoscope is inserted in the horse's nose and observations are made. To diagnose upper airway conditions that are only apparent during exercise, the horse is exercised on a high-speed treadmill and endoscopy is performed during exercise. This method is highly technical, and can only be performed in referral centers.
In human medicine, spectrogram analysis of speech is a large field of study, and practical applications of this field, including speech therapy and voice recognition, are now commonplace (Kent, R D, Vocal Tract Acoustics, "J. Voice", 7:97-117 (1993)). In addition, spectrogram analysis of sound has been used in many animal species, including songbirds (Lindell C., Limited Geographic Variation in the Vocalizations of a Neotropical Furnariid, Synallaxis albescens "Wilson Bull", 110:368-374 (1998)) and marine mammals (Hanggi, E B, Schusterman, R J, Underwater Acoustic Displays and Individual Variation in Male Harbour Seals, Phoca vitulina, "Anim. Behav.", 48:1275-1283 (1994)).
Respiratory sounds of horses have been recorded using a radiostethoscope (Attenburrow et al, Resonant Frequency of the Lateral Ventrical and Saccule and "Whistling", "Equine Exerc. Physiol.", pages 27-32 (1990)). These sounds were analyzed using spectrogram analysis. However, respiratory sounds recorded using a radiostethoscope placed over the trachea do not directly relate to the respiratory sounds of exercising horses.
In the related art, U.S. Pat. No. 4,218,584 to Attenburrow describes a stethoscope for detecting and recording data from a horse while the horse is walking, trotting, cantering, jumping and galloping. The invention includes a transducer, such as a microphone which is attached to the animal's skin adjacent the windpipe. The electrical output from the transducer is transferred to a radio transmitter mounted on the animal or its harness. The radio transmitter can transmit signals a distance from the horse to allow for monitoring the breathing at a distance.
Also, of interest is U.S. Pat. No. 4,720,866 to Elias et al which describes a method and apparatus for acquiring, analyzing and displaying stethoscopic data using a microcomputer. The stethoscopic data come from lung sounds, not upper airway sounds as recorded in the invention described therein. The invention includes a means for providing an audio signal. The audio signal is pre-amplified and conditioned for application to a bank of fixed-center-frequency electronic filters. The output of each filter is sampled and converted to digital form. The output is then processed in a computer for analysis and display on a CRT screen or recording in a hard copy device.
U.S. Pat. No. 5,165,417 to Murphy, Jr. describes a diagnostic method and apparatus for detecting breathing abnormalities in humans to diagnose lung (not upper airway) disorders. The system includes means for receiving the sound signal from the patient, means for conditioning the sound signal to attenuate normal sounds and means for storing a sample sound signal. The system may also include means for digitizing the sound signal, means for amplifying the sound signal, means for determining an average signal value of at least a portion of the sound signal, and means for generating a threshold value based on that average value. Further included may be means for sequentially comparing the sound waves with the predetermined time interval to identify an initial deflection wave having a duration falling within the time interval, means responsive to the means for sequentially comparing the sound waves, for sequentially comparing the sound waves following the initial deflection wave to the threshold value, and means for identifying an adventitious sound occurring within the sound signal only when a plurality of consecutive sound waves including the initial deflection wave have an amplitude at least as large as the threshold value.
U.S. Pat. No. 5,737,429 to Lee describes a portable, visible and audible stethoscope. The stethoscope includes a sound absorbing cup having a microphone and an output device. In use, the sounds from the human body are converted into electrical signals by microphone. The electrical signals are amplified in the output device and supplied to the speaker of the output device to produce an audio signal. The amplified electrical signals are also supplied to the oscilloscope to produce a graph representing the electrical signals.
Only of minimal interest is U.S. Pat. No. 5,503,141 to Kettl et al which shows a microphone mounting structure which permits conversion of a conventional respirator into a sound amplifying respirator. The invention uses a microphone responsive to oral sounds within the respiratory mask and produces electrical signals indicative of these oral sounds. The system also includes an amplification circuit which provides output sounds representative of the oral sounds which the microphone detects within the mask.
There remains the need for a method and apparatus for recording the upper airway respiratory sounds of a horse during exercise which is portable and easy to use and which allows for analysis of the respiratory sounds to determine whether the horse has an upper airway condition.